Problem: $ { \left[\begin{array}{rr}{1} & {2} \\ {3} & {-2} \\ {-2} & {1}\end{array}\right]+\left[\begin{array}{rr}{-1} & {-1} \\ {3} & {-2} \\ {3} & {3}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{1}+{-1} & {2}+{-1} \\ {3}+{3} & {-2}+{-2} \\ {-2}+{3} & {1}+{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{0} & {1} \\ {6} & {-4} \\ {1} & {4}\end{array}\right]}$